DEGRADATION OF TCE BY IRON MINERALS AND AQUIFER MATERIALS

Trichloroethylene (TCE) is one of the more toxic and most frequently detected groundwater contaminants. Natural attenuation of TCE through biological degradation has been extensively studied and is widely accepted to contribute to TCE degradation. It is still unclear, however, whether abiotic degradation of TCE by reduced iron (Fe) minerals, natural organic matter, and reduced sulfur species contributes to natural attenuation. Of these reactions, reduction by reduced Fe minerals has been discussed as a particularly promising pathway for natural attenuation of chlorinated solvents. In particular, magnetite, a common mixed-valent Fe mineral, has been suggested to be responsible for TCE attenuation at some field sites despite slow rates of TCE reduction by magnetite observed in laboratory experiments. Here we measured the reduction of TCE by magnetite, clay minerals, and soil samples collected from a TCE plume at the Middlefield-Ellis-Whisman (MEW) site in California. We tracked TCE loss, as well as accumulation of products, including dichloroethenes, acetylene, ethene, and ethane in sterilized, untreated, and amended microcosms. We used DNA biomarkers for dehalogenating organisms to determine if TCE degradation pathways were predominantly biotic or abiotic. In addition, we characterized the aquifer samples using wet chemical extractions, X-ray diffraction, and ⁵⁷Fe Mössbauer spectroscopy. Our work provides insight into how aqueous Fe (II) and sulfide impact abiotic reduction of TCE by Fe-minerals and Fe-bearing sediments.